1. Field of the Invention
This invention relates in general to logging tools for detecting parameters of fluid flows, and in particular to a logging tool for detecting flow parameters of multiphase fluid flow.
2. Description of the Prior Art
Prior art logging tools have been utilized for detecting flow parameters for different types of fluid flows. For example, well logging tools are frequently used within producing oil and gas wells for detecting flow rates for different fluid flow components being produced within petroleum wells. Prior art production logging tools have frequently included spinner types of flowmeters having an impeller which is caused to rotate when immersed within a flowstream. Such flowmeters include fullbore flowmeters and deflector flowmeters. Additionally, production logging tools have included other tools for detecting downhole densities and pressures of production fluids.
Prior art water holdup meters have been provided by utilizing well logging tools which work by detecting the dielectric constant of the produced fluids. This particular type of water holdup tool operates under the principle that different fluids have different dielectric constants. Typically, electrodes are provided within a tool housing, and the electrodes are disposed about a longitudinal axis of a logging tool. The electrodes are connected to a capacitance measurement means which detects the net dielectric constant for fluids flowing within the central portion of a well immediately about the tool housing.
This type of prior art logging tool has several limitations. One is that the tool does not work properly if the water holdup becomes so high that the water phase becomes continuous. In that case, such as a flow of a mixture of oil and water with the oil dispersed as bubbles in a continuous water medium, the high conductivity of the water masks varying dielectric effects that are attributable to the changes in the volumetric fraction of the oil included within the oil and water mixture. Another problem occurs in that only the dielectric constant of the central portion of the well is measured. Very often flow will vary across a section of the well, especially in deviated wells. In fact, in highly deviated wells, such as horizonal wells, the fluid flow may become stratified across a cross-sectional area of the well. This may result in prior art fluid holdup tools detecting only a small portion of the stratified flow, such as only one phase, and not the other portions of the flow of produced fluids.
Further, different flow patterns may be present both in vertical flow and horizontal flow. In horizontal flow, very often bubble flow, and elongated bubble flow will occur. Additionally, stratified flow, wave flow, slug flow, annular and annular mist flow, and dispersed froth flow may occur depending on the different flow parameters and flow velocities encountered. Vertical flow patterns may also include bubble flow, froth flow, annular, annular mist flow, and slug flow. These different flow patterns occur depending on the velocities, the cross-sectional diameter, and other such parameters affecting flow rate. Typically the volumetric proportions which occur at downhole well conditions are much different than those that occur further uphole, as well as on the surface. This is affected by the amount of gas which stays in solution and other such similar type of phenomenon.
Typically, different densities, frictional parameters and different phases for different constituents of segregated multiphase fluid flow result in different flow rates for the different constituents. For example, in a segregated, multiphase flow in a producing well having flow constituents which consist of oil, gas and water, the gas phase may flow faster than the oil phase, which may flow faster than a water phase. In fact, in some sections of wells having multiple zones of production, one phase may flow in an opposite direction within the well to that of a net flow of fluids. When annular type of flow segregation occurs, such as with slug, annular mist, and froth flow, only the flow occurring within the central portion of a cross-sectional area of a well is detected. Very often the flow occurring around an outer circumference of the well is not detected by prior art well logging tools, such as the capacitance type of water holdup meter discussed above.